The present invention relates to a discharge lamp lighting device suitable for a projection type display such as a liquid crystal projector.
High voltage discharge lamps such as metal halide lamps or high-pressure mercury lamps are used as light sources of projection type displays because it is easy for these lamps to obtain high conversion efficiency close to that of point sources. Dedicated discharge lamp lighting devices for supplying voltages and currents required for lighting are used to light the high voltage discharge lamps.
An AC type high voltage discharge lamp is typically once DC-driven for a fixed time by a timer circuit, and then shifted to be AC-driven. In the related art, however, the time between the operation of an igniter circuit and the lighting of the lamp fluctuates due to conditions of the high voltage discharge lamp (e.g. lamp temperature) or variations in the ease of lighting peculiar to the discharge lamp. Accordingly, there is a disadvantage that the time for the discharge lamp to be DC-lit is so short that the discharge lamp is shifted to be AC-lit as its arc remains unstable, and the discharge lamp is blacks out thus.
In addition, the related-art discharge lamp can be activated even if there is a failure such as I/O short-circuit in a power control circuit. Accordingly, there is a disadvantage that a circuit located after the power control circuit, such as an igniter circuit, or the discharge lamp is broken in a chain reaction.
It is a first object of the invention to provide a discharge lamp lighting device which can light a high voltage discharge lamp quickly and stably regardless of the conditions or variations of the discharge lamp.
It is a second object of the invention to provide a discharge lamp lighting device which can prevent electric circuits or the like located after a power control circuit from being broken in a chain reaction even if there is a failure such as I/O short-circuit in the power control circuit. A discharge lamp lighting device having: a power control circuit for controlling power to be supplied to a discharge lamp;
In order to achieve the first object, according to a first aspect of the invention, there is provided a discharge lamp lighting device having: a power control circuit for controlling power to be supplied to a discharge lamp; an AC converter circuit provided between the power control circuit and the discharge lamp for converting a DC current into an AC current; a timer circuit for controlling operation of the AC converter circuit; and an igniter circuit for generating a high voltage pulse to thereby activate the discharge lamp.
The timer circuit includes: a second timer for starting as a timer in accordance with a power supply activating signal; a first timer for starting as a timer in accordance with lighting of the discharge lamp; and an OR circuit for outputs of the first and second timers.
In order to achieve the second object, according to a second aspect of the invention, there is provided a discharge lamp lighting device having: a power control circuit for controlling power to be supplied to a discharge lamp.
The discharge lamp lighting device further has: a lamp voltage detection terminal for detecting a lamp voltage of the power control circuit; and a protection circuit which is provided so that when a lamp voltage detection signal is outputted from the lamp voltage detection terminal, the protection circuit suspends activation of the discharge lamp even if a lamp-switching-on signal is supplied, and so that when no lamp voltage detection signal is outputted from the lamp voltage detection terminal, the protection circuit allows activation of the discharge lamp in accordance with a lamp-switching-on signal supplied to the protection circuit.